Oils or fats including edible oil are in great demand every day as the principal materials for foods, cooking and so forth, therefore, a determination of the degree of oxidation or deterioration of oils or fats is a daily requirement from the viewpoint of hygiene and sanitation, tastes and odors of foods manufactured or cooked, or the like.
When an oil or fat is oxidized or deteriorated, it generally is accompanied by an unpleasant odor. So, the degree of oxidation or deterioration of an oil or fat may be, to some extent, judged by smelling. However, such judgement requires skills and besides is never expected to be accurate. For a judgement of the degree of oxidation or deterioration of an oil or fat, determination of peroxide value, carbonyl value, acid value, TBA value (to be determined by adding 2-thiobarbituric acid to a sample oil or fat, heating the mixture, removing the oil layer with the aid of chloroform, determining the absorbance at 532 m.mu. of the aqeous layer, and calculating the milligrams of malonic aldehyde equivalent to the absorbance per 1 kg of the sample oil or fat), etc. is usually conducted, and other than this no proper judging method is to be found today.
However, operations for such determination of the values need some technical skills as well as experimental apparatus, and moreover they are rather troublesome for ordinary people, and accordingly the determining operations are not compatible with usual kitchen or factory works.